C-axis alignment of an oxide film over an oxide semiconductor film

Abstract

The stability of a step of processing a wiring formed using copper, aluminum, gold, silver, molybdenum, or the like is increased. Moreover, the concentration of impurities in a semiconductor film is reduced. Moreover, the electrical characteristics of a semiconductor device are improved. In a transistor including an oxide semiconductor film, an oxide film in contact with the oxide semiconductor film, and a pair of conductive films being in contact with the oxide film and including copper, aluminum, gold, silver, molybdenum, or the like, the oxide film has a plurality of crystal parts and has c-axis alignment in the crystal parts, and the c-axes are aligned in a direction parallel to a normal vector of a top surface of the oxide semiconductor film or the oxide film.

What is claimed is: 
     
       1. A semiconductor device comprising:
 a gate electrode over a substrate; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film over and in contact with the gate insulating film, the oxide semiconductor film comprising In, Ga, and Zn; 
 an oxide film over and in contact with the oxide semiconductor film, the oxide film comprising In, Ga, and Zn; 
 a pair of electrodes over and in contact with the oxide film, the pair of electrodes comprising copper; 
 a pixel electrode electrically connected to one of the pair of electrodes; and 
 a liquid crystal layer over the pixel electrode, 
 wherein the oxide film includes a plurality of crystal parts and has c-axis alignment in the plurality of crystal parts, 
 wherein c-axes are aligned in a direction parallel to a normal vector of a top surface of the oxide semiconductor film or the oxide film, 
 wherein a proportion of Ga atoms in the oxide film is higher than a proportion of Ga atoms in the oxide semiconductor film, and 
 wherein, in an atomic ratio of the oxide film, Ga is larger than In, and Zn is larger than Ga. 
 
     
     
       2. The semiconductor device according to  claim 1 , wherein the gate insulating film comprises a first insulating film and a second insulating film provided on the first insulating film. 
     
     
       3. The semiconductor device according to  claim 2 , wherein the first insulating film is a nitride insulating film. 
     
     
       4. The semiconductor device according to  claim 2 , wherein the second insulating film is an oxide insulating film. 
     
     
       5. The semiconductor device according to  claim 1 , wherein the pair of electrodes is in contact with a top surface of the gate insulating film. 
     
     
       6. A semiconductor device comprising:
 a gate electrode over a substrate; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film over the gate insulating film, the oxide semiconductor film comprising In, Ga, and Zn; 
 a pair of electrodes over the oxide semiconductor film, the pair of electrodes comprising copper; 
 an oxide film provided between the oxide semiconductor film and the pair of electrodes, the oxide film comprising In, Ga, and Zn; 
 a pixel electrode electrically connected to one of the pair of electrodes; and 
 a liquid crystal layer over the pixel electrode, 
 wherein the oxide semiconductor film has a channel formation region, 
 wherein the pair of electrodes is electrically connected to the oxide semiconductor film through the oxide film, 
 wherein a proportion of Ga atoms in the oxide film is higher than a proportion of Ga atoms in the oxide semiconductor film, and 
 wherein, in an atomic ratio of the oxide film, Ga is larger than In, and Zn is larger than Ga. 
 
     
     
       7. The semiconductor device according to  claim 6 , wherein the gate insulating film comprises a first insulating film and a second insulating film provided on the first insulating film. 
     
     
       8. The semiconductor device according to  claim 7 , wherein the first insulating film is a nitride insulating film. 
     
     
       9. The semiconductor device according to  claim 7 , wherein the second insulating film is an oxide insulating film. 
     
     
       10. The semiconductor device according to  claim 6 , wherein the oxide film includes a plurality of crystal parts and has c-axis alignment in the plurality of crystal parts. 
     
     
       11. A semiconductor device comprising:
 a gate electrode; 
 a gate insulating film over the gate electrode; 
 an oxide semiconductor film over the gate insulating film, the oxide semiconductor film comprising In, Ga, and Zn; 
 a pair of electrodes over the oxide semiconductor film, the pair of electrodes comprising copper; 
 an oxide film provided between the oxide semiconductor film and the pair of electrodes, the oxide film comprising In, Ga, and Zn; 
 a pixel electrode electrically connected to one of the pair of electrodes; and 
 a liquid crystal layer over the pixel electrode, 
 wherein the oxide semiconductor film has a channel formation region, 
 wherein the pair of electrodes is electrically connected to the oxide semiconductor film through the oxide film, 
 wherein a proportion of Ga atoms in the oxide film is higher than a proportion of Ga atoms in the oxide semiconductor film, 
 wherein, in an atomic ratio of the oxide film, Ga is larger than In, and Zn is larger than Ga, and 
 wherein the liquid crystal layer is configured to be driven by an FFS mode. 
 
     
     
       12. The semiconductor device according to  claim 11 , wherein the gate insulating film comprises a first insulating film and a second insulating film provided on the first insulating film. 
     
     
       13. The semiconductor device according to  claim 12 , wherein the first insulating film is a nitride insulating film. 
     
     
       14. The semiconductor device according to  claim 12 , wherein the second insulating film is an oxide insulating film. 
     
     
       15. The semiconductor device according to  claim 11 , wherein the oxide film includes a plurality of crystal parts and has c-axis alignment in the plurality of crystal parts.